A fuel cell stack has a structure wherein a plurality of basic structures (fuel battery single cells) each having an anode-side electrode, an electrolyte membrane, and a cathode-side electrode, are stacked and connected in series. The fuel battery single cell which is the basic structure has a structure wherein the anode-side electrode is placed on one surface of the electrolyte membrane comprising a polymer ion exchange membrane, the cathode-side electrode is placed on the other surface thereof, and the resulting structure is sandwiched by separators. A plurality of the fuel battery single cells each having such a structure are stacked and connected in series, and the stacked structure of the plurality of fuel battery single cells is sandwiched from both sides in the stack direction by a pair of current-collector plates, a pair of insulating plates, and a pair of end plates, so that the obtained structure is used as a fuel cell stack which generates a high voltage.
Here, in each fuel battery single cell, a manifold hole is formed in the electrolyte membrane and the separator. When the anode-side electrode, electrolyte membrane, and cathode-side electrode are sandwiched by the separators, the manifold holes of the electrolyte membrane and the separators are connected, and there is created a fuel battery single cell in which a part of a manifold to be described later is formed. When a plurality of the fuel battery single cells are stacked and connected in series to create the fuel cell stack, the manifold holes are connected between the fuel battery single cells. In other words, the parts of the manifold to be described later formed in the fuel battery single cells are connected. With this structure, in the fuel cell stack created by the stack of the fuel battery single cells, a manifold for supplying or discharging a fuel gas or an oxidizing agent gas between the outside of the fuel cell stack and the fuel battery single cells, and a manifold for supplying or discharging a coolant (for example, cooling water) between the outside of the fuel cell stack and the fuel battery single cells for suppressing temperature increase due to heat generation in the fuel battery single cells are formed through the fuel battery single cells in the direction of stacking.
In the fuel cell stack, with the above-described structure, the fuel gas and the oxidizing agent gas are supplied from a side of one end plate of the fuel cell stack through the manifold for gas supply to each fuel battery single cell, and, after the supply, gas is discharged from each fuel battery single cell to the manifold for gas discharge, and the discharged gas is discharged to the outside through the manifold for gas discharge from the side of the one end plate.
In the fuel battery single cell having the above-described structure, hydrogen, which serves as the fuel gas supplied to the anode side, and oxygen, which serves as the oxidizing agent gas supplied to the cathode side, electrochemically react through the electrolyte membrane, and water is produced. The produced water is drained from the fuel cell stack along with the discharge gas through the gas discharge manifold extending through the stack comprising the plurality of fuel battery single cells.
In order to achieve a superior performance for water discharge from the fuel cell stack, for example, Patent Documents 1-3 disclose placement of the fuel cell stack in an inclined manner with respect to a horizontal surface, to thereby, achieve a downward inclination in the manifold inside the stack.    Patent Document 1: JP 2004-207106 A    Patent Document 2: JP Hei 5-174862 A    Patent Document 3: JP 2004-146303 A